Development of TLP-AI Technology to Realize High Temperature Operation of Power Module

Application of SiC power devices is regarded as a promising means of reducing the power loss of power modules mounted in power control units. Due to those high thermostable characteristics, the power module with SiC power devices are required to have higher operating temperature than the conventional power module with Si power devices. However, the limitations of current packaging technology prevent the utilization of the full potential of SiC power devices. To resolve these issues, the development of device bonding technology is very important. Although transient liquid phase (TLP) bonding is a promising technology for enabling high temperature operation because its bonding layer has a high melting point, the characteristics of the TLP bonding layer tend to damage the power devices. This paper describes the development of a bonding technology to achieve high temperature operation using a stress reduction effect. Called transient liquid phase bonding with an aluminum interlayer (TLP-AI), this method utilizes the high melting point and ductility of aluminum to reduce the device stress of power modules. The developed method lowers device stress by approximately 44% compared to conventional TLP bonding. After a thermal cycling test (-40°C ⇔ 175°C, 3,000 cycles) no cracks were observed in the aluminum interlayer. Moreover, after a power cycling test (30°C ⇔ 175°C, 100,000 cycles), crack propagation was reduced by approximately 80% compared to conventional solder bonding.